Bifunctional and regenerable molecular electrode for water electrolysis at neutral pH

The instability of molecular electrodes under oxidative/reductive conditions and insufficient understanding of the metal oxide-based systems have slowed down the progress of H-2-based fuels. Efficient regeneration of the electrode's performance after prolonged use is another bottleneck of this research. This work represents the first example of a bifunctional and electrochemically regenerable molecular electrode which can be used for the unperturbed production of H-2 from water. Pyridyl linkers with flexible arms (-CH2-CH2-) on modified fluorine-doped carbon cloth (FCC) were used to anchor a highly active ruthenium electrocatalyst [Ru-II(mcbp)(H2O)(2)] (1) [mcbp(2-) = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine]. The pyridine unit of the linker replaces one of the water molecules of 1, which resulted in RuPFCC (ruthenium electrocatalyst anchored on -CH2-CH2-pyridine modified FCC), a high-performing electrode for oxygen evolution reaction [OER, overpotential of similar to 215 mV] as well as hydrogen evolution reaction (HER, overpotential of similar to 330 mV) at pH 7. A current density of similar to 8 mA cm(-2) at 2.06 V (vs. RHE) and similar to-6 mA cm(-2) at -0.84 V (vs. RHE) with only 0.04 wt% loading of ruthenium was obtained. OER turnover of >7.4 x 10(3) at 1.81 V in 48 h and HER turnover of >3.6 x 10(3) at -0.79 V in 3 h were calculated. The activity of the OER anode after 48 h use could be electrochemically regenerated to similar to 98% of its original activity while it serves as a HE cathode (evolving hydrogen) for 8 h. This electrode design can also be used for developing ultra-stable molecular electrodes with exciting electrochemical regeneration features, for other proton-dependent electrochemical processes.

Automated summary

In this study, a bifunctional and electrochemically regenerable molecular electrode was successfully developed for the stable production of hydrogen. By anchoring a highly active ruthenium electrocatalyst onto modified fluorine-doped carbon cloth, the electrode exhibited high activity for both oxygen evolution reaction and hydrogen evolution reaction in acidic conditions. The electrode design showed excellent electrochemical regeneration performance after prolonged use.